1. Field of the Invention
The present invention relates to delivery servers, content delivery methods for the delivery servers, booster servers, and content delivery methods for the booster servers. The present invention particularly relates to a delivery server, for example, which transmits content to a booster server and a transmission command including information on the booster server to a client terminal so that the content is transmitted from the booster server to the client terminal when a delivery server is not available for a delivery request transmitted from the client terminal. Accordingly, a delivery service business may be started in a small way using the delivery server.
2. Description of the Related Art
In recent years, a construction of an NGN (Next Generation Network) which is obtained by replacing a telephone network of a line switching system in the related art by a network based on an P (Internet Protocol) technique has been promoted. The NGN has band ensuring function and a security function. In the NGN, session control is performed using an SIP (Session Initiation Protocol).
In such an NGN, a client terminal receives content such as a video image or music delivered from a delivery server. In this case, it is difficult to recognize the number of delivery requests transmitted from the client server and determine a server resource necessary for the transmitted delivery requests.
For example, Japanese Unexamined Patent Application Publication No. 2004-110277, Japanese Unexamined Patent Application Publication No. 2005-327155, and Japanese Unexamined Patent Application Publication No. 2004-7228 disclose systems in which a delivery server (content provision server) transmits content such as a video image or music to a client terminal (user terminal) through a network such as the Internet.
FIG. 18 shows streaming deliveries in which image pickup data is delivered from a camera server 210 serving as a delivery server through a network 230 to client terminals 220a to 220c. The number of streaming deliveries performed by the single camera server 210 is limited due to capability of a CPU (Central Processing Unit), for example. When streaming deliveries which maintain high image qualities are performed, the number of deliveries is more strictly limited.
In order to obtain the increased number of deliveries, load distribution techniques have been proposed. An example of the load distribution techniques includes load distribution employing a DNS (Domain Name System) shown in FIG. 19. In this load distribution technique, when a client terminal 220 requests a DNS server 240 to transmit IP addresses of delivery servers, the DNS server 240 assigns IP addresses to the delivery servers, i.e., delivery servers 0 to 2 (delivery servers 210a to 210c) and transmits the assigned IP addresses to the client terminal 220. In this way, load applied to each of the delivery servers is reduced.
Furthermore, an example of the load distribution techniques includes load distribution employing a load balancer (switch) shown in FIG. 20. In this load distribution technique, when a client terminal 220 requests a DNS server 240 to transmit IP addresses of delivery servers, the DNS server 240 transmits information on an IP address of a load balancer 250 to the client terminal 220, and the load balancer 250 successively assigns IP addresses to delivery servers 0 to 2, i.e., delivery servers 210a to 210c. In this way, load applied to each of the delivery servers is reduced.
Furthermore, in order to increase the number of deliveries, a multicast method has been proposed in recent years. Examples of the multicast method include an IP multicast and application level multicast.